Soldiers are required to rapidly acquire, identify, and accurately fire on enemy targets and may use weapon-mounted sights with visible and infrared light sources generated by one or more lasers to produce collimated beams of light for use in daytime and nighttime missions. These sights may be mounted on small arms such as the M4A1 carbine and other weapons and are used to provide better target observation, illumination, and marking. Coaligned visible and infrared lasers may be boresighted to assist in operation of the weapon. Unlike visible lasers, infrared lasers are only viewable with a night vision device, a phosphorescence material, thermal imager, or other device of similar function. Coaligning visible and infrared lasers allows a soldier to boresight the infrared laser of a weapon mounted sight using just the visible laser (i.e. without the need for a night vision device to see the infrared light beam).
An optical bench sub-assembly located within a weapon mounted housing may be used to hold the electrical and optical components of the coaligned and collimated lasers. The housing may provide protection from unintended contact or debris. The housing may be coupled to a weapon with a suitable attachment mechanism, for example a rail grabber, slide-lock mechanism, or other clamp.
Mechanical adjustors extending through the housing and in contact with the optical bench sub-assembly may be used to steer the optical axis of the coaligned light beams relative to the housing. This may enable a user to boresight the previously coaligned light beams to some reference, such as a point of impact of a projectile at a known distance or a barrel mounted boresight laser.
The degree of coalignment between two collimated lasers can be quantified by measurement tools and expressed as an angle, typically given in thousandths of a radian (mRad). The degree of coalignment accomplished by passive, snap-together mechanical designs, that is designs which do not employ active feedback, are limited by a tradeoff between size and the precision of the components used. For example, the coalignment of a weapon mountable snap-together design might be realistically limited to about 15 mRad. For effective use at ranges of 200-800 meters, substantially better coalignment, e.g. less than 2.0 mRad, is desired which typically requires an active alignment scheme that employs feedback from a measurement device and adjustable compensators during the coalignment process.